Of course level indicator lights don't work so I rely on toilet giving a little burp when getting full. Busy with grandkids etc I wasn't paying attention and realized it had been several weeks since I dumped black water tank. When I pulled lever nothing came out until I started flushing . I think the valve must be letting water slowly leak out. Do I need a new valve or is there something else I can try. I thought maybe paper was sticking to it it. I dumped in water softener , dawn , flushed and flushed, still doesn't seem to hold water.